Method of extrusion-fusion welding of lead parts through an aperture in a battery case

ABSTRACT

The present invention provides a novel method of extrusion-fusion welding of lead parts through an aperture in a battery case which uniformly controls the area of contact between members to be welded at the completion of the extrusion process in order to produce consistent, high-quality welds exhibiting higher strength and superior durability.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 948,979, filed Oct. 5,1978.

This application is also a continuation-in-part of my prior U.S. patentapplication Ser. No. 790,881, filed Apr. 26, 1977, now U.S. Pat. No.4,166,210 issued Aug. 28, 1978, and entitled "ELECTRODES FOR USE IN THEEXTRUSION-FUSION WELDING OF LEAD PARTS THROUGH AN APERTURE IN A BATTERYCASE AND METHOD OF EXTRUDING, FUSING AND FORGING LEAD CONNECTIONS INBATTERY CASES" which application is incorporated by reference as iffully set forth herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods of making intercellwelds in electric storage batteries and in particular to those methodswhere electrodes are oriented on either side of a partition or otheraperture in a battery case, lugs or other battery parts are placed overeach side of that aperture, contact produced therebetween, currentpassed through the lead parts to melt the same and pressure appliedgenerally for the purpose of providing an electrical connection throughthe aperture. Such an apparatus is disclosed in U.S. Pat. No. 4,013,864.

It is long known that lead parts on either side of a partition with anaperture formed therein can be welded through that aperture using anyoneof a number of techniques. In the lead acid battery art, the most commonsite for welding through an aperture is during the formation ofintercell connections, that is, in making the electrical connectionsbetween one battery cell and the next and/or between the end mostbattery cells and the exterior battery terminal of the battery. Sinceconnections through apertures of this sort, in addition to beingelectrical, must provide a liquid seal from cell to cell to prevent"pumping", some attention has been directed in the concerning variousmethods for insuring that an intercell connector, in addition toproviding a good electrical connection, will also exhibit good sealingcharacteristics.

U.S. Pat. No. 3,687,734, generally discloses a connector forelectrically connecting two elements of a storage battery through anaperture wherein at least one of the connectors lugs is provided with apassage extending therethrough. Molten material from an external portionof the connector exists through this passage during the heat fusion stepas a result of pressure from a heat energy build up. The patenteeattempts by this structure to avoid the problem of blow outs or leadexpulsion which has been encountered by many practitioners in this art.

Another attempt to avoid "blow out" is disclosed in U.S. Pat. No.3,476,611, wherein an intercell connections are by a projection weldingprocess from pins which extend through the partition between twoadjacent battery compartments, which pins have dimensions such that,when they are fluidized during the process, the volume of the pinmaterial does not exceed the volume defined by the walls of the opening.

Such attempts inherently involve tolerance and positioning problemsduring the manufacturing and assembly of the parts in battery. Morerecently, other methods have been developed for producing batteryintercell electrical connections, which methods have generally beenreferred to as "extrusion-fusion" type method. For example, in U.S. Pat.No. 3,793,086, a method is disclosed wherein flat surface connector lugsare placed on each side of the battery partition wall, adjacent anaperture. The connector lugs are extruded by a pair of opposedelectrodes into the aperture until they meet, whereupon an electricalwelding current is applied. When the welding current ceases, theconnectors are allowed to cool. As stated in this patent, "it should beemphasized that reduction of the initially applied shear force duringthe welding cycle is essential. If the high applied shear force ismaintained during the welding cycle, molten lead will be squirted fromthe welding joint and an imperfect joint can result."

Another approach to the problem of "blow outs" is that disclosed, forexample, in U.S. Pat. No. 4,046,062, wherein separate hold down sleevesare employed to clamp the lugs into sealing engagement with thepartition wall aperture prior to and during the extrusion-fusionprocess. After clamping, metal is extruded until contact is made,electric current is then passed through the extruded metal to melt it,and, under the continuing force of the electrodes, metal is caused toflow into any voids in the aperture while, at the same time, extrudingmore metal out of the lugs into the aperture until the aperture ispacked full of lug metal.

In U.S. Pat. No. 3,896,316, a similar extrusion-fusion system isdisclosed wherein high density polyurethane pads are provided aroundeach of the electrodes to clamp the lugs tightly against the walls ofthe intercell connection during the extrusion, fusing the cooling steps.

In U.S. Pat. No. 3,723,699, the problem of blow outs or lead expulsionis expressed in a projection welding context wherein the lugs areprovided with upstanding annular ribs which surround the hole in thepartition wall and are caused to bite into the partition wall, in anattempt to minimize flow and to provide a good mechanical key betweenthe lugs and partition wall, thus minimizing the possibility of relativesliding movement between the lugs and partition wall.

Accordingly, as seen from the above described prior art references,considerable problems have been experienced with blow outs, particularlywhere lead is extruded into the aperture of the partition with theintent of filling the same. Extrusion-fusion welding processes have nonethe less achieved considerable success in the industry.

Since the development of extrusion-fusion welding processes, otherproblems have also been encountered in controlling the types of weldswhich are obtained under actual production conditions in battery plants.It is long been known, for example, that variations in such parametersas the electrical welding current, squeezing pressure, and in thedimensions of the connector lugs and/or the partition or casing wallthickness has a direct effect on the quality of the weld. In the past,these parameters were adjusted and the resulting welds were theninspected to determine the quality thereof. This adjustment andinspection process continued until welds meeting the predeterminedcriteria were obtained.

After this initial set up procedure, which can be very time consumingand laborious, an attempt is then made to maintain these parametersconstant throughout the subsequent production. Unfortunately, changes inone or more of these parameters during the ensuing production could havea detrimental effect on the quality of the welds produced thereby. Insome cases, these welds will tend to over heat and blow out, while inother cases, cold or incomplete welds may be formed.

Although, as stated above, a number of conditions may account for thevariability from weld to weld, I have found that the condition of thelugs contribute substantially to the great variability in weldperformance. Lugs are typically cast of lead alloys which harden as theyage, and, which during the preceding battery manufacturing operationsmay acquire varying surface characteristics. For example, lugs which arecast in conventional parts molding machines may have a slight residue ofoil or other film which adheres thereto from the casting machines (as,for example, films used to aid in the release of the parts which arecast).

Lugs may also age in the battery plants for varying lengths of timedepending upon their sequence of use. During storage they may be exposedto varying quantities of lead oxide dust and/or other contaminentspresent in the battery plant, and may be subjected to various additionalcontaminents depending upon the operations employed to fuse those lugsto their respected straps. In some battery manufacturing plants, thelugs may be cast in a "cast-on" machine or may otherwise be formed andfused to the straps with a much lesser degree of aging prior to thefinal battery assembly.

Once associated with the groups, the lugs are particularly prone tocontamination as a result of shedding or other direct or indirectexposure to the active material of there associated groups or elements.Finally, depending upon the manufacturing process employed to make thecases, variable contaminations of the lugs surfaces routinely occurs.

Prior art extrusion-fusion techniques, to the extent they have attemptedto control parameters of surface contamination, tend to rely on sensingthe establishment of an electrical current path through the lugs at ornear the completion of the extrusion process, that is, at the timecontact is created between the lugs within cellular aperture.Unfortunately, variations in surface contaminations of the lugsconsiderably change the surface resistance of the lugs; therefore,methods in which the establishment of a certain degree of electricalcontact within the aperture is sensed, tend to begin the weld cyclerelatively earlier or later depending upon how dirty the lug surfacesare at their points of contact, i.e., how much lug contact area need beestablished in order to trigger the weld cycle.

Other prior art methods have focused upon controlling the pressure ofextrusion to thereby presumably establish a uniform contact area betweenthe lugs, regardless of there surface contamination. Due to thevariability aging processes however, and the consequent variations inthe hardness of the lugs to be extruded (depending upon the age of thoselugs), close control of the extrusion pressure from weld to weld resultsin variations of contact area between the lugs.

Other prior art methods have used mechanical stops to limit theextrusion of the extruding apparatus in order to establish a uniformcontact area between the lugs. However, variations in lug dimensionswill effect the contact area thereby rendering this technique less thansatisfactory.

SUMMARY OF THE INVENTION

The present invention generally relates to a novel method ofextrusion-fusion type welding lead parts through an aperture in the wallof a battery case, and more particularly, a method, the use of whichobviates the necessity for time consuming, laborious set up procedures,variable pressure control, separate clamps, or particular lug oraperture configurations, and which produces an extremely homogeneousweld with a uniform grain structure and surprising strength heretoforeunknown and unachievable in battery manufacture.

The superior characteristics of the welds (and batteries producedtherewith) result from numerous features incorporated in applicantsnovel method. One such feature is the novel electrode tip used inperforming the method of applicant's invention. Applicant has recognizedthat the extrusion portion of the electrode, that is, the tip portionwhich initially upsets the metal to cause the initial contact thereofwithin the aperture, should be disposed generally away from a forgingportion, that is, a portion which, in addition to other functions, tendsto limit the extrusion of the electrode during the cold extrusion phase,whereby the degree of metal-to-metal contact within the aperture isuniformly limited.

Applicant has also found that by providing the electrode tip with anannular forging portion surrounding the aperture in order to forge thelug around the aperture at least during the aperture filling compressionprocess, the problem of blow-outs is eliminated and a substantiallydenser, stronger, gas-free, homogeneous weld is attained. To theembodiment of the electrode tip, which is preferred for carrying outapplicants novel method, the annular forging portion is configured witha contacting surface which is forced into the lug in order to create asealing zone of high compression leads surrounding the aperture. Theforging portion also includes an inner beveled surface whichadditionally forges lead adjacent to the high compression sealing zonetoward the central axis of the aperture. The annular forging portionfurther acts as a cold heat sink for lead disposed adjacent to thatportion of the electrodes, to prevent the melting of same.

Applicant has found that it is not necessary to use differentialpressures during the initial upsetting and subsequent compressionprocesses. Accordingly, far greater lug, partition and aperturetolerances are established so that weld powers, hold times and holdpressures exhibit substantially greater latitudes then heretoforeexhibited by prior art methods.

Accordingly, a primary object of the present invention is the provisionof a novel battery having intercell welds exhibiting superior strengthand quality.

Another object of the present invention is a method for extrusion-fusiontype welding for forming intercell welds through an aperture in a leadacid storage battery wherein the degree of metal-to-metal contact withinthe aperture is uniformly limited to a predetermined magnitude prior tofusion.

A further object of the present invention is the provision of a methodfor producing intercell welds in automotive storage batteries whileovercoming attendant problems with blow-out.

An additional object of the present invention is the provision of anextrusion-fusion type method for forming intercell welds in a lead acidstorage battery wherein significantly greater lug, partition andaperture misalignments may be suitably accommodated without readjustingto compensate for same.

These and other objects of the present invention will become apparentfrom the following more detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the preferred embodiment electrode ofthe present invention.

FIG. 2 is a cross section of the portion of a battery showing flat lugsdisposed on either side of an intercell partition with an apertureformed therein and with two preferred embodiment electrodes similar tothat illustrated in FIG. 1 above shown disposed in stand by positionsspaced apart from the lugs and oriented axially with the aperture of thepartition through which the intercell connection is to be formed.

FIG. 3 is a cross section similar to the view shown in FIG. 2, whereinthe electrodes have been moved into contact with the lugs and have begunto extrude portions of those lugs into the aperture formed in theintercell partition.

FIG. 4 is a greatly enlarged cross section similar to FIGS. 2 and 3wherein the electrodes have proceeded with the extruding step to a pointwhere metal-to-metal contact between the lugs is established within theaperture and at a point where the contacting surface of the forgingportions of the electrodes have contacted the lugs.

FIG. 5 is a cross section similar to FIGS. 2 and 3, wherein fluidizationof lead within the aperture has been effected and the electrodes boughtfurther together so that the molten metal fills the aperture.

FIG. 6 is a cross section similar to FIGS. 3-5, wherein the connectionis complete and the electrodes have been withdrawn therefrom, showingthe completed weld configuration.

FIG. 7 is a perspective view of a strap and lug showing the externalappearance of a lug in which an intercell connection in accordance withthe present invention has been made.

FIG. 8 is a cross section similar to FIG. 6 wherein the compressiveforces exerted on the lugs in accordance with the method of the presentinvention are schematically represented by lines and arrows.

DETAILED DESCRIPTION OF THE DRAWINGS

Although specific forms of the invention have been selected forillustration in the drawings, the following description is drawn inspecific terms for the purpose of describing these forms of theinvention, this description is not intended to limit the scope of theinvention which is defined in the appended claims.

The present invention relates to a method of welding lead or lead alloylugs through an aperture in a wall of a battery case, as for example,through an aperture in an intercell partition of a battery case toproduce an intercell connection, or alternatively, through an exteriorwall of the battery case to form a battery terminal. This methodbasically comprises positioning the lugs on opposing sides of theaperture to least entirely overlap the aperture, extruding at least aportion of the lugs into the aperture to touch within the aperture,passing current through the lugs to melt portions of the lugs at leastwithin the aperture, compressing at least the melted portions within theaperture to fill the aperture and forging unmelting portions of the lugssurrounding the aperture at least during a portion of the compressionstep to prevent blow out of the melted portion during compression.

Referring now to FIG. 1, there is shown the preferred embodiment of anelectrode tip, generally referred to as 10, used to carry out the methodof the present invention. Electrode 10 comprises a conical extrusionportion 12 having a vertex 14. The conical extrusion portion 12 issurrounded by a concentric, circular forging portion 16 having acontacting surface 18, which is more clearly shown in FIGS. 2-6. Boththe conical extrusion portion 12 and the forging portion 16 are disposedon one end of a cylindrical body 20. The conical extrusion portion 12 ispreferably positioned coaxially with the cylindrical body 20 with theplane of the contacting surface 18 being substantially perpendicular tothe coincident axes.

A jaw mount 22 is provided on the opposite end of the cylindrical body20 from the conical extrusion portion 12 and forging portion 16 in orderto enable the electrode to be conveniently mounted on welding jaws (notshown). As shown more clearly in FIG. 2, the forging portion includes anouter beveled surface 24 and an inner beveled surface 26 both of whichslope away from the contacting surface 18. The outer beveled surface 24results from the inclusion of a draft on the outer end surface of theforging portion 16. In the preferred embodiment, the draft angle is 3°.The inner beveled surface 26 terminates in a recess 28, the surface ofwhich is substantially perpendicular to the axis of the cylindrical body20. It has been imperically determined that the angle of the innerbeveled surface 26 can range between 3° and 15° and still be effectivein minimizing weld blow outs as will be subsequently described. In thepreferred embodiment, the angle is between 5 and 8 degrees.

A surface 27 extends from the base of the conical extrusion portion 12to the surface of the recess 28 at a draft angle which, in the preferredembodiment, is equal to 3°. The distance between the base of the conicalportion 12 and the surface of the recess 28 is substantially equal to1/16 of an inch in the preferred embodiment. The electrode 10 isconstructed of a material having good electrical conductivity andhardness characteristics.

Referring now to FIG. 2, there is shown a cross section of a portion ofa battery partition 30 having an aperture 32 to form therein and havinglugs 34 and 36 disposed there against to overlap the aperture 32. Theorientation of the electrodes, designated generally 38 and 40, withrespect to the aperture prior to welding is also illustrated. The lugs34 and 36 are shown to comprise generally flat surfaces which may lie upagainst the complimentally opposing surfaces of partition 30. The lugsare selected to be of a width and height so that precise alignment withrespect to the aperture 32 is not necessary. The importance of this factresides in part upon the fact that each lug 34 and 36 is formed or castas part of straps 42 and 44 respectively, which, although not shown, arewelded to a plurality of battery plates which make up a group ofelements of the battery and which, during the assembly process, areslipped into the case generally in the direction shown by arrows a and bin FIG. 2, so that portions of the lugs 34 and 36 overlap the partitionaperture 32.

It will also be noted from FIG. 2 that the use of lugs 34 and 36 withflat surfaces disposed thereon allow the finished groups to be inserteddown into the case without fear that any particular portion of the lugswill hang up on the partition, and further without the problemsattendant with projection welding techniques for first getting thegroups into the battery cells and then for positioning the projectionsin the aperture, as more fully described for those techniques in U.S.Pat. No. 3,364,076.

As seen in FIG. 2, the electrodes designated generally 38 and 40 arealigned substantially coaxially with aperture 32. The conical extrusionportions 12a and 12b terminate in vertexes 14a and 14b for initiallycontacting the lugs and for extruding the same into the aperture 32. Thediameter of the base of the conical extrusion portion 12 issubstantially equal to the diameter of the aperture 32. However, whenused in a production environment, it may be necessary to make thediameter of the base smaller than the diameter of the aperture in orderto compensate for misalignment due to production alignment tolerances.

A misalignment, wherein a portion of the conical extrusion portionoverlaps a portion of the edge of the aperture, can cause pinching andplastic inclusions in the weld which detrimentally effect the quality ofthe weld. Consequently, the phrase "substantially equal to" is intendedto include differences in diameters which are necessitated by practicalimplementation considerations such as compensation for productionalignment tolerances. In the embodiment preferred for carrying out themethod of the present invention, when welding through an aperture havinga diameter substantially equal to 7/16 of an inch, the diameter of thebase of the conical extrusion portion is substantially equal to 3/8 ofan inch. With a base diameter equal to 3/8 of an inch, the height of thevertex 14 should lie within a range of 1/32 of an inch to 3/32 of aninch and is preferably 1/16 of an inch. The range of heights has beenemperically determined and relates to the functional requirements of theconical extrusion portion 12 necessary to carry out the method of thepresent invention, as will be hereinafter described.

The diameter of the concentric, circular forging portion must be smallenough to preclude overhanging an edge of the lug, but large enough toprevent overlapping any portion of the aperture edge in order tominimize blow outs in the weld and also large enough to stall furthercold extrusion of the lugs, both of which features relate to steps inthe method of the present invention and will be more fully describedhereinafter. The diameter should fall within the range of 1/2 to 5/8 ofan inch. In the embodiment preferred to carry out the method of thepresent invention, the diameter of the circular contacting surface 18 issubstantially equal to 5/8 of an inch. As shown in FIG. 2, threadedbores 50 and 52 are additionally provided in each electrode to receivethreaded shafts for mounting electrode to welding jaws (not shown).

As previously stated, the electrode should be of sufficient hardness toexhibit acceptable durability during the lead and lead alloy workingprocesses to which they are to be subjected. For this purpose, number 25beryllium copper is the preferred material from which the extrusionportion 12 and forging portion 16 may be milled or otherwise formed.

Referring now to FIG. 3, electrodes 38 and 40 have begun to movetogether in the directions of arrows C and D to a point where theconical extrusion portions 12a and 12b have begun to contact lugs 34 and36 into extruded portions 34a and 36a of those lugs into the aperture32. The conical shape of the extrusion portion 12 causes the lugmaterial to be forced into the aperture and away from its center, awedge-like effect which tends to fill the aperture with lug material.This effect is further illustrated in FIG. 8 where lines and arrows,collectively referred to as 80, schematically show the compressiveforces exerted on, for example, lug 36, by the conical extrusion portion12 of the contacting electrode 10. At the position illustrated in FIG.3, the contacting surfaces 18a and 18b of the forging portions 16a and16b have not yet begun to contact the lugs 34 and 36.

FIG. 4, which is greatly enlarged cross section similar to FIG. 3,illustrates the continued movement of the electrodes together to a pointwhere the contacting surfaces 18a and 18b of the forging portions 16aand 16b have contacted the surfaces of the lugs 34 and 36 and areslightly embedded therein at which point further movement of theelectrodes is stalled. In the embodiment of the electrodes preferred tocarry out the method of the present invention, the contacting surfacesbecome embedded to a depth equal to about 0.005" before the movement ofthe electrodes actually stops. At this point, extruded portions 34a and36a have made the desired degree of contact within the aperture 32. Theforce applied to the electrodes 38 and 40 which urges them in thedirections indicated by the arrows e and f is of such a magnitude thatthe extrusion portions 12a and 12b will extrude the hardest of the lugsto be welded, while at the same time being insufficient to overcome thestalling effect of the forging portions 16a and 16b in the softest oflugs after the contacting surfaces 18a and 18b of the forging portions16a and 16b have made contact with the surfaces of the lugs 34 and 36respectively. In the preferred embodiment, with the diameter of thecontacting surface being equal to 5/8 of an inch, this force issubstantially equal to 680 pounds.

The stalling effect of the forging portions 16a and 16b effectivelylimits the extrusion movement of each of the electrodes to the axialdistance measured from the vertex 14 of the extrusion portion 12 to theintersection of the plane containing the contacting surface 18 with theaxis of the electrode. In the preferred embodiment, this distance issubstantially equal to 1/2 the thickness of the battery partition 30.When used for welding through battery partitions having nominalthickness of 0.070 inch, the contacting surface 18 is 0.035 inch fromthe vertex 14. Accordingly, it may be seen that for this phase of theprocess, the relative thickness of the lugs 34 and 36 are immaterial tothe proper functioning of the extruding portions 12a and 12b andtherefore the proper contacting area will always be formed within theaperture upon engagement of the contacting surfaces 18a and 18b with thelugs 34 and 36 respectively.

After the proper contact area has been established between the lugportions 34a and 36a, a current is applied by the electrodes through thelugs in order to fluidize the lead within the aperture. This current isapplied immediately upon the establishment of the proper metal-to-metalcontact area within the aperture in the movement of the electrodestogether continues in a smooth and uninterrupted fashion as shown inFIG. 5. There it may be seen that the forging portion 16a and 16b, incombination with the extrusion portions 12a and 12b, have continued tomove together in the directions E and F to force the lead to completelyfill the aperture 32 in the partition 30. In the preferred embodiment,each electrode continues to move for a distance substantially equal to0.025 inch.

As previously stated, the relationship of the height of the conicalportion 12 to the diameter of its base, a relationship which defines theincluded angle or sharpness of the cone, has been empericallydetermined. For the base diameter of 3/8 of an inch, the sharpest conehas a height of 3/32 of an inch and the flattest has a height of 1/32 ofan inch. It has been found that sharper cones, cannot adaquatelyfunction to follow in and hydraulically fill the aperture with fluidizedlead in accordance with the method of the present invention, since theforging portion would bottom out before the aperture has become filled.This creates voids or "worm holes" which have a detrimental effect onthe quality of the weld. In addition, the greater height of the conecauses a deeper depression 76 (see FIG. 7) in a lug which would tend toweaken the completed weld. In addition, it has been found that flattercones do not permit the uniform establishment of the proper initialcontact within the aperture. Also, an entirely flat extrusion portionwas found to cause plastic inclusions in the weld as well as non-uniforminitial heat contact area.

It should be noted that as the aperture 32 is being filled with lead,the forging portions 16a and 16b are further embedded into the exteriorsurfaces of the lugs 34 and 36. In the preferred embodiment, thecontacting surface 18 of each electrode becomes embedded in the lug fora total depth of approximately 0.030 inch. This penetration of thecontact surfaces 18a and 18b of the forging portions 16a and 16b intothe surfaces of the lugs 34 and 36 respectively, during fluidization ofthe lead within the aperture, will prevent the expulsion of molten leadfrom the aperture, commonly known as "blow-out".

At the present time, it is not fully understood how the forging portions16a and 16b act within this environment to eliminate problems of blowout. It is theorized that the circular contacting surface 18 whichsurrounds the aperture produces an annular zone of high compression leadwhich acts as a seal preventing lead expulsion from the weld zone. Thisis schematically shown by the lines and arrows 82 in FIG. 8 whichrepresents the compressive force exerted by the circular contactingsurface 18.

It is further theorized that the inner beveled surface 26 of the forgingportion 16, in acting to form or force that portion of the luginteriorly adjacent the contacting surface 18 toward the weld zones,sets up stresses internally within the lug which additionally act toconfine the weld nuggets to prevent expulsion. This is schematicallyshown by the lines and arrows 84 of FIG. 8, which represent thecompressive forces exerted by the inner beveled surface 26 of theforging portion 16. Finally, the depth of the recess 28 between theextrusion portion 12 and the forging portion 16 is believed to provide acertain degree of relief for leads squeezed between the electrodes, andthat lead may actually be forged up into the annular recess 28 in theelectrode rather than be expulsed from the weld zone.

Referring now in particular to FIG. 6, wherein the electrodes 38 and 40are being withdrawn in the direction G and H respectively, to reveal afinished weld, may be seen that the final intercell connectiondesignated generally 70 is extremely homogeneous and completely lackingin the air pockets or "worm holes" which typify welds produced by priorart methods. At the present time, it is also not understood why themethod of the present invention consistently produced weld nuggetswhich, upon sectioning and etching to show grain structure, exhibit anextremely wide weld zone 72 which is generally disposed in theconfiguration shown in FIG. 6.

In FIGS. 6 and 7, the final configuration of the intercell connectionproduced in accordance with the method of the present invention isclearly illustrated. This intercell connection is, as aforesaid,characterized by large uniform weld nugget 72 which is disposed tocompletely fill the aperture 32 within the partition 30. Annulardepressions 74a and 74b which have been formed by the forging portions16a and 16b of the electrodes 38 and 40 respectively, are seenencircling the center of the connection, while central concave, conicaldepressions 76a and 76b are disposed in the center of the intercellconnection.

In order to determine the comparative strengths of the intercell weldillustrated in FIG. 6, the weld produced using the method of the presentinvention was tested against conventional welds produced by prior artmethod using a "stepped electrode". Shear tests were conducted onstandard lead and antimony lugs which were welded with similar currentsthrough partition apertures. In all instances a 31/4 inch air cylinderwas utilized in order to provide shearing force across the lug on oneside of the partition while the lug on the other side of the partitionwas rigidly held. The values obtained by these tests represent the airpressure applied to the 31/4 inch cylinder and, accordingly, areproportional to the pounds of shear force supplied to each intercellconnection in order to break it. Intercell connections produced usingthe prior art method employing the "stepped electrode", are found toshear generally at between 100 to 120 pounds of air pressure. Bycomparison, intercell connections produced by the method of the presentinvention utilizing the preferred embodiment electrode describedtherein, generally sheared between about 190 to 200 pounds of pressure.Accordingly, the use of applicants invention enabled the formation ofintercell welds which are not sensitive to dimensional irregularities inthe lugs to be welded or the precise alignment of those lugs withrespect to the apertures through which the intercell connection is to bemade.

It will be understood that various changes in the details, materials andarrangement of parts which have been herein described and illustrated inorder to explain the nature of this invention may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the following claims.

What is claimed is:
 1. A method of welding lead parts through anaperture in a wall of a battery case utilizing an electrode comprisingat least an extruding portion for extruding portions of said parts totouch within said aperture, and a contacting portion for contactingother portions of said parts during the welding of said parts,comprising the steps of:a. positioning said parts on opposite sides ofsaid aperture to at least entirely overlap said aperture; b. extrudingat least a portion of said parts into said aperture at least until saidcontacting portion contacts a surface of said part and said extrudedportions touch within said aperture; c. limiting the degree of contactbetween said parts within said aperture responsive to the degree ofcontact between said contacting portion and said lead part; d. passingcurrent through said parts to melt said portions of said parts at leastwithin said aperture; and e. compressing at least said melted portionswithin said aperture.
 2. The invention of claim 1 further comprising thestep of forging unmelted portions of said parts surrounding saidaperture at least during a portion of said compressing step.
 3. Theinvention of claim 2 wherein said forging step forms an annulardepression surrounding said aperture.
 4. The invention of claim 2wherein at least a portion of said unmelted portion is sheared duringsaid forging step.
 5. The invention of claim 2 wherein at least aportion of said unmelted portion is formed generally toward saidaperture during said forging step.
 6. The invention of claim 1 whereinthe limiting provided by the performance of step c is responsive to thedistance between the leading surface of the extruding portion and theleading surface of the contacting portion.
 7. The invention of claim 6wherein the distance is substantially equal to 1/2 the thickness of thebattery wall.
 8. The invention of claim 6 wherein the limiting providedby the performance of step c occurs substantially irrespective of thethickness of the lead parts.
 9. The invention of claim 1 wherein thelimiting provided by the performance of step c is provided bytemporarily stalling movement of the electrodes.
 10. The invention ofclaim 1 wherein the performance of step d forms a conical depression.11. The invention of claim 1 wherein at least a portion of said meltedportions are formed generally toward said aperture boundary during saidcompressing step.